The present invention relates to a filter used in a filtering device for removing particles floating in liquids or in the air and to a method for manufacturing the same.
For filters for removing particles floating in liquids or in the air, sand, gravel, or metal nets or fibrous materials of paper, cloth, resin, glass or metals have been conventionally used. However, these were incapable of withstanding use over extended periods of time due to the fact that they tended to clog and lacked durability. A filter which is capable of operation over an extended period of time by reverse cleaning and which is rugged and durable has been proposed as shown in FIG. 1. This filter is obtained by helically winding a profile metal wire A for a filter at a constant spacing d, axially disposing metal bars B for securing space inside the cylinder formed by the metal wire A, and welding the profile metal wire A for a filter and the metal bars B for securing space at their cross points. However, due to the limits imposed by the techniques involved in the manufacturing method, this filter is defective in that it is impossible to obtain uniform fine slits of less than 40.mu. with precision and economy. The obtainable slit space is 50-100.mu. at best and the slit space is not uniform.
Another kind of filter has also been used which is obtained by winding a filter wire at constant spacing on a core body of a polygonal metal pipe. However, a winding machine capable of providing a uniform slit space of less than 40.mu. is not available. With the best winding machine, it is only possible to obtain a filter having variation of about .+-.50.mu..
As another method, a filter wire with resin coating is wound around a core body of a polygonal metal pipe so that each turn is in contact with adjacent turns. The resin coating is dissolved by a suitable solvent for obtaining a slit space. However, with this method, it is difficult to coat the resin uniformly on the wire with a thickness of several microns to 20.mu.. Thickness variations of 8-10.mu. are generated even with the best coating method obtainable. Thus, this method has also proven unsuitable for obtaining uniform slit spaces due to irregular thickness of the coated resin. Furthermore, when the resin coating is dissolved in a suitable solvent, the core body and the filter wire are loosened and the slit space is disturbed. Thus, this method is also defective in that a uniform space within the range of less than 40.mu. is hard to obtain with precision.